The other question this tragedy brings up (again, unfortunately) is how do we protect ourselves from monsters like this without sacrificing some of our freedoms?

You're right, it cannot be done, and it's idiocy to try; we seem to try nonetheless. If we make our rules based on the hideous actions of those who entirely lack a moral compass, all we achieve is putting limits on the just people who make up the vast majority of the population.

In this country we spend trillions of dollars to regulate for things that, in the end, we cannot truly be protected from.